Evolution is not confined to the distant past. By comparing genomes across time and examining sequential fossil layers, biologists can detect heritable change in lineages and document how populations continue to diverge.

What “genomic change” shows about ongoing evolution

Genomes preserve a record of ancestry because DNA is inherited with occasional heritable alterations. When those alterations spread through reproduction, populations become measurably different over time.

Genomic change can be detected directly by sequencing and comparing DNA from:

• Individuals in the same population sampled at different times (time-series genomics)

• Closely related species (to identify accumulated differences)

• Ancient DNA (when preserved) versus modern descendants or relatives

Common genomic patterns that indicate change through time

• New variants appear and persist: unique substitutions or small insertions/deletions that are inherited in later generations

• Gene duplication and divergence: duplicated genes accumulate differences, sometimes leading to new or specialised functions

This figure shows how an ancestral gene can duplicate, creating two copies in the same genome that can then evolve independently. Over time, mutations can cause the duplicates to diverge, potentially leading to new or specialized gene functions (paralogs). Source

• Changes in noncoding DNA: shifts in regulatory regions can alter gene expression patterns without changing protein sequences

• Chromosomal changes: inversions or translocations can reduce recombination in certain regions, allowing sets of linked variants to persist together

How the fossil record documents continuous change

Fossils occur in ordered geological strata, so older forms are generally found in deeper layers and younger forms in more recent layers.

Stratigraphic columns summarize rock layers in vertical order, making it possible to read relative time from bottom (older) to top (younger). This type of diagram helps explain why fossils in deeper strata typically represent earlier forms in a lineage, while fossils higher up represent more recent forms. Source

When multiple fossils from successive layers show incremental shifts in anatomy, this provides a physical timeline of change within a lineage.

What “continuous change” looks like in fossils

• Stratigraphic sequences showing gradual modification of structures (e.g., changes in limb proportions or skull features across layers)

• Transitional features that combine traits seen earlier and traits common later, consistent with descent with modification

• Species turnover across time: appearance, persistence, and disappearance of forms in the same region as environments shift

Linking genomic change with the fossil record

Genomic and fossil evidence are strongest when they converge on the same historical pattern:

• Relative timing agreement: lineages that diverge earlier in the fossil record typically show deeper genomic differences than lineages that diverge later

• Trait evolution with genetic correlates: when a trait changes through a fossil sequence, related modern organisms often show differences in genes or regulatory regions tied to that trait’s development

• Lineage continuity: fossils document morphological continuity, while genomes document heritable continuity, together supporting ongoing evolution rather than isolated, unconnected appearances

Important limitations to interpret carefully

• Fossilisation is selective: many organisms and environments rarely preserve fossils, creating gaps

• Rates vary: some lineages show long periods of little visible change, while others show faster shifts; genomic change may accumulate even when morphology appears stable

• DNA preservation is rare: ancient DNA is exceptional and usually limited to relatively recent fossils